Many different food products are packed in ready made plastic cups which on top of heat sealed aluminium or plastic lids have cover lids (snap on lids) which are locked around the top part of the cups.
In order to apply the cover lids to the cups it is necessary to lift the cups from the turntable in rotating machines or lamellas in straight line machines, this is done in cassettes which are inserted in holes in the supporting plates, see FIG. 1.
The cassettes are known to have been made from aluminium or stainless steel. In recent years the trend has been towards stainless steel cassettes as steadily increasing demands for hygienic production has led to the use of more and more aggressive cleaning agents, which have a bad effect on aluminium parts.
30 Most cups used for packing of food products are produced by vacuum forming from heated plastic sheets as this type of cups are low cost compared to injection moulded cups. But the vacuum forming process does not ensure that the sealing rims of the cups have the same thickness all around.
35 The plane surfaces of the top of the metallic cassettes and of the heating plates cannot compensate for the difference in thickness, for that reason in prior art rubber rings have been known to be inserted in the metallic cassettes extending above the metallic surface making a flexible support under the rim of the cup, see FIG. 2.
From a hygienic point of view, metallic cassettes are not a good solution as there will always be a cavity between the cassettes and the supporting plate which cannot be properly cleaned.
To overcome this problem it is known that for a straight line machine the lamellas with cassettes have been milled from blocks of stainless steel, this solves the hygienic problem but is an extremely costly process.
Another disadvantage with the purely metallic cassettes is the noise created by the heating surface being brought at high speed against an unyielding surface. Packing machines are often built to handle cups with different top sections, in the dairy industry most machines are built to operate with round cups with top diameters 95 or 75 mm. The industry is interested in equipment with shortest possible time lost when changing from one cup size to the other.
To meet this demand machines have been built where the lamella with cassettes are lifted off the machines conveyor chains into a magazine, and other lamellas with cassettes for the other cup size are lowered from another magazine onto the conveyor chains. Such a system adds enormously to the price of the machine as well as representing down-time where no production is carried out.
An example on a method and a device used previously are shown in U.S. Pat. No. 3,759,013 which discloses a method and apparatus for sealing aluminum containers comprising a plurality of annular cup retaining inserts mounted in rows and columns on a conveyor-like platform, each insert having a resilient sealing ring with substantially L-shaped cross-section fixedly attached to its upper surface and extending vertically downward along the internal vertical wall of the insert. A row of heat sealing heads, each having a horizontally disposed heat sealing face located at its lower extreme, is located above the conveyor-like platform, and each heat sealing head is concentrically aligned with and immediately above a correspondingly positioned container and insert at the sealing station.
Hence, an improved cassette would be advantageous, and in particular a more efficient and/or reliable system for handling cups would be advantageous.